Lifting Beam (Below-The-Hook Lifting Device) 2

[JP20]

I've been tasked with designing a lifting beam. I am studying/going through ASME BTH-1-2017. Regarding pinned connections in chapter 3, there is (4) modes of failure. The first three modes are tensile strength, single plane fracture, and double plane shear strength... the formulas yield an answer in Kips. Is this the ALLOWABLE FORCE acceptable on each pinned connection/area? I assume so but I wanted to get someone else's opinion who may have been over this already. Just want to make sure.. any help would be much appreciated. For what it's worth, IMO, they poorly word some (a lot) of what's in this book.

ASME BTH-1-2017 & ASME B30.20-2018

J

 

[r13]

The resulting forces are nominal capacity of the element under consideration. The capacity then is used to compared to the magnified real lift load - total lift weight and effects * FOS (factor of safety) (This is wrong, see discussions below)

 

[JAE]

I have the 08 version - it is all based on allowable stress (or strength actually) design using a safety factor Nd in the equations.

If 2017 hasn't changed over to LRFD-type design (which I doubt it has) then your results are the maximum allowable capacity of each limit state.
Read through the early parts of the document (chapter 1) and where they define Nd.

 

[Lomarandil]

Also not familiar with the 2017 version, but can vouch that in previous editions, the resulting answer would be the allowable capacity in real terms.
(I suspect just as JAE does -- lifting and rigging calcs will probably outlast geotechnical engineering in the hold-out against changing to LRFD. Superintendants and riggers generally don't want to be concerned with factored load combinations. They want to know it's safe and will double something up if they're not sure about it.)

As JAE said, Nd is your safety factor, so no additional load factors or magnification needed as retired13 suggested.

----
just call me Lo.

 

[r13]

Yes, I agree the above correction. I switched the safety factor in the equation. (Nominal Capacity/FOS = Allowable Working Load)

 

[dhengr]

JP20:
Why don’t you draw the ASME sketch (Fig. C3-3, 2008 Ed.) of their Pin-Connected Plate (and the appropriate notation) for each of the potential failure modes they want you to check, and explain how they would work and/or fail? This would probably help you understand what they are driving at, what the intended failure mechanism is. In fact, these very sketches should be part of our calc. sheets covering each of these conditions.

 

[JP20]

This was a question that needed a yes or no answer.

The safety factors (Nd) are already built in to the equations.

I suppose Lo had the best answer. And I take that as a “yes”, the resulting load (in kips) (minimum from all three formulas) is what what we can apply to each pinned connection and be ok.

 

[Lomarandil]

Sorry, sometimes we like to hear ourselves talk.

(Or more charitably, we've learned that it often reduces the back-and-forth nature of internet engineering to get into some of the rationale and caveats behind yes and no.)

----
just call me Lo.

 

[JAE]

JP20,
Sorry if we (I) mis-interpreted your question:

Is this the ALLOWABLE FORCE acceptable on each pinned connection/area?

Your use of BOLD to highlight the word ALLOWABLE led me to believe you were asking whether this was allowable or ultimate design.
(vs. asking whether you take the lowest value of the various limit states which is pretty basic engineering procedure)

 

[JP20]

Lol.. understandable.. thank y'all!

 

[JP20]

JAE,

I wasn't asking if I take the lowest of the three limit states - I was asking if the value figured (in kips) by the three formulas was the allowable force from the cable/shackle for each pinned connection.

 

[JAE]

JP20 - Please forgive me here but I still don't quite understand what you are asking. I don't see how Lomarandil answered any differently than I did.

Could you expand a bit on what you mean by: "...the allowable force from the cable/shackle for each pinned connection."?

If you aren't asking whether this is and allowable vs. ultimate condition, then I'm not sure what you are looking for.
Your original question was: "Is this the ALLOWABLE FORCE acceptable on each pinned connection/area?"

A pinned connection is a shackle pin extending through an eye hole in a plate essentially. Are you suggesting that the kips value given in the three formulae might be for each side of the pin vs. the whole assembly?

 

[JP20]

I think you are overthinking it or something. See my quick sketch below.. the "F" value - What I was asking is: Is the number yielded from one of those three equations the allowable "F"?

 

[Craig_H]

Just to further poke the "this was a yes/no question" bear...
- The allowable load on a pinned connection on a BTH lifting device not exposed to a combined stress state will the the lowest value calculated for the Tensile / Single Plane Fracture / Double Plane Fracture / Bearing. It's generally quite simple to optimize the design so that one of these failures does not significantly limit the capacity of your shackle/lug connection. I think that the text at the start of 3-3.3.1 is actually quite clear in that respect. This also gives you a good picture of your anticipated failure mode, which is nice for specifying periodic NDT inspections and the points of interest for that testing to investigate.
- Have a read of the next clause, 3-3.3.2. In the case of your multihole lifting beam, some configurations of it will induce significant flexural tensile stresses, and could also involve significant shear stresses in the vicinity of the lug hole. That effect requires consideration, and will lower your shackle connection capacity.

 

[Lomarandil]

I don't see how Lomarandil answered any differently than I did.

I really didn't, we're in agreement. I only chimed in to back up your view versus the mistaken response above.

----
just call me Lo.

 

[Settingsun]

JP20, which F value do you want from your sketch? They're not equal because the upper force is inclined while the lower is vertical. Do you want the lower F as that is the weight being lifted?

 

[JP20]

Either one

 

[JP20]

All I was wondering is if the value calculated from any one of those three equations is the max force that may be applied safely. (Disregarding all other modes of failure)

 

[dhengr]

JP20:
The smallest force or load produced by those three conditions specific formulas controls, and is the max. force/load which should be applied to that detail in order to comply with the std. Note that your detail of a single plate standing on edge, and with pin holes along both the top and bottom edges of the plate is quite a different detail than that shown in in Fig. C3-3, and should be analyzed and designed accordingly. Then, you introduce several new design considerations to the whole problem, beam bending and shear, combined stresses, etc.

So, “All I was wondering is if the value calculated from any one of those three equations is the max force that may be applied safely. (Disregarding all other modes of failure)” seems to be a mixed-up statement/question. You really should draw the sketches of Fig. C3-3 which I suggested in my first post, for each of the conditions, and study them, and understand the failure mechanism they are looking at, to see how they compare/relate to your problem. Then, don’t disregard other modes of failure. Also, watch the finished quality of your plated edges and the drilled holes.

 

[dik]

Is anyone aware of a design example that goes through the entire process of a lifting beam, lifted at midpoint and with loads at each end that addresses strength, LTS, BTH and safety issues?

There seems to be numerous questions about the design of this type of structure.



Dik